Exhaust purification device

ABSTRACT

Provided are gas dispersion portion  7 C covering entry end face of selective reduction catalyst  4  (aftertreatment device) and introducing exhaust gas  1  through exhaust feed port  11  from direction substantially perpendicular to axis of aftertreatment device and mixing pipe  7 B (exhaust conduit) curved from exhaust feed port  11  in the gas dispersion portion  7 C toward exit side of the selective reduction catalyst  4  to extend axially of aftertreatment device. Gas dispersion portion  7 C is of crushingly deformed shape to ensure area from exhaust feed port  11  to vicinity of extension of axis of the selective reduction catalyst  4  as fan-likely spreading flow guide space  12,  remaining area being flat throttling space  13  close to entry end face of selective reduction catalyst  4.  Boundary between throttling and flow guide spaces  13  and  12  in crushing deformed shape is formed as arc-like taper slope  14.

TECHNICAL FIELD

The present invention relates to an exhaust emission control device.

BACKGROUND ART

It has been recently proposed that a particulate filter for capturingparticulates in exhaust gas is incorporated in an exhaust pipe and aselective reduction catalyst capable of selectively reacting NO_(x) withammonia even in the presence of oxygen is arranged downstream of theparticulate filter, urea water as reducing agent being added at aposition between the selective reduction catalyst and the particulatefilter, thereby attaining lessening of both the particulates and NO_(x).

Such addition of the urea water to the selective reduction catalyst isconducted at the position between the particulate filter and theselective reduction catalyst. Thus, in order to ensure sufficientreaction time for pyrolysis of the urea water added to the exhaust gasinto ammonia and carbon dioxide gas, it is necessary to prolong adistance between the urea-water added position and the selectivereduction catalyst. However, arrangement of the particulate filter andthe selective reduction catalyst in a substantially spaced apartrelationship will extremely impair the mountability on a vehicle.

In order to overcome this, an exhaust emission control device compact insize as shown in FIG. 1 has been proposed. In such exhaust emissioncontrol device, incorporated in an exhaust pipe 2 through which exhaustgas 1 flows from an engine is a particulate filter 3 housed in a casing5 to capture particles in the exhaust gas 1; arranged downstream of andin parallel with the particulate filter 3 and housed in a casing 6 is aselective reduction catalyst 4 having a property capable of selectivelyreacting NO_(x) with ammonia even in the presence of oxygen. An exit endof the particulate filter 3 is connected to an entry end of theselective reduction catalyst 4 through an S-shaped communication passage7 such that the exhaust gas 1 discharged from the exit end of theparticulate filter 3 is reversely curved back into the entry end of theadjacent selective reduction catalyst 4.

The communication passage 7 is the S-shaped structure comprising a gasgathering portion 7A which covers the exit end of the particulate filter3 to gather the exhaust gas 1 just discharged from the exit end of theparticulate filter 3 through substantially perpendicular turnabout ofthe gas, a mixing pipe 7B which extracts the gathered exhaust gas 1 fromthe gathering portion 7A in a direction reverse to the exhaust flow inthe particulate filter 3 and a gas dispersing portion 7C which coversthe entry end of the selective reduction catalyst 4 to disperse the gas1 guided by the mixing pipe 7B through substantially perpendicularturnabout of the gas into the entry end of the selective reductioncatalyst 4. The entry end of the mixing pipe 7B is centrally providedwith an injector 8 for addition of the urea water into the mixing pipe7B and directed to the exit end of the mixing pipe 7B.

In the example illustrated, arranged in the casing 5 and in front of theparticulate filter 3 is an oxidation catalyst 9 for oxidizationtreatment of the exhaust gas 1, and arranged in the casing 6 and behindthe selective reduction catalyst 4 is an ammonia lessening catalyst 10for oxidization treatment of surplus ammonia.

With such construction being employed, the particulates in the exhaustgas 1 are captured by the particulate filter 3. The urea water is addeddownstream of the filter and intermediately of the mixing pipe 7B intothe exhaust gas 1 by the injector 8 and is pyrolyzed into ammonia andcarbon dioxide gas, so that NO_(x) in the exhaust gas 1 is favorablyreduced and depurated by the ammonia on the selective reduction catalyst4. As a result, both the particulates and NO_(x) in the exhaust gas 1are lessened.

In this case, the exhaust gas 1 discharged from the exit end of theparticulate filter 3 is reversely curved back by the communicationpassage 7 into the entry end of the adjacent selective reductioncatalyst 4 so that a long distance is ensured between the urea-wateradded position intermediately of the communication passage 9 and theselective reduction catalyst 4 to ensure enough reaction time forproduction of ammonia from the urea water.

Moreover, the particulate filter 3 is arranged in parallel with theselective reduction catalyst 4 and the communication passage 7 isarranged between and along the particulate filter 3 and selectivereduction catalyst 4 so that the whole structure becomes compact in sizeto substantially enhance its mountability on a vehicle.

As a prior art literature pertinent to this kind of exhaust emissioncontrol device, there already exists, for example, the following PatentLiterature 1.

CITATION LIST Patent Literature

Patent Literature 1: JP 2008-196328A

SUMMARY OF INVENTION Technical Problems

However, in such turnabout introduction of the exhaust gas 1 into theselective reduction catalyst 4, the exhaust gas 1 tends to flow biasedlyto outward of the curved direction upon the turnabout of the exhaust gas1, which may lead to non-uniform introduction of the exhaust gas 1 intothe selective reduction catalyst 4 and resultant insufficient derivationof catalytic performance to be inherently exerted.

It has been also proposed as an improved measure that the gas dispersionportion 7C has a depression in a position opposite to an introductionside of the exhaust gas 1 and directed toward an entry end face of theselective reduction catalyst 4 to suppress the flow of the exhaust gas1. Nevertheless, it is a fact that any depression shapes proposed up tothe present may correct longitudinal bias in flow along the introduceddirection of the exhaust gas 1 into the gas dispersion portion 7C, butcannot concurrently contribute to improved dispersion in a lateraldirection (direction substantially parallel to the entry end face of theselective reduction catalyst 4 and substantially perpendicular to theintroduced direction of the exhaust gas 1).

The invention was made in view of the above. Upon turnabout introductionof exhaust gas into a selective reduction catalyst or otheraftertreatment device, the invention has its object to correct moreeffectively than ever before a tendency of the exhaust gas flowingbiasedly and relatively much to outward of a curved direction to therebyattain improvement in catalytic performance.

Solution to Problems

The invention is directed to an exhaust emission control device with anexhaust system including an aftertreatment device for purifying exhaustgas passing therethrough and with an adopted layout for turnaboutintroduction of the exhaust gas into said aftertreatment device,characterized in that it comprises a gas dispersion portion for coveringan entry end face of said aftertreatment device and for introducing theexhaust gas thereinto through an exhaust feed port from a directionsubstantially perpendicular to an axis of said aftertreatment device andan exhaust conduit curved from the exhaust feed port in said gasdispersion portion toward an exit side of said aftertreatment device toextend axially of said aftertreatment device, said gas dispersionportion being of a crushingly deformed shape to ensure an area from saidexhaust feed port in said gas dispersion portion to a vicinity of anextension of the axis of said aftertreatment device as a fan-likelyspreading flow guide space, a remaining area being a flat throttlingspace close to the entry end face of said aftertreatment device, aboundary between said throttling and flow guide spaces in the crushinglydeformed shape being formed as an arc-like taper slope.

In this way, the exhaust gas guided through the exhaust conduit ischanged in direction into the direction substantially perpendicular tothe axis of the aftertreatment device and is introduced into the exhaustfeed port. Thus, during its flowing from said exhaust feed port throughthe fan-likely spreading flow guide space, dispersibility in the lateraldirection (direction substantially parallel to the entry end face of theaftertreatment device and substantially perpendicular to the introduceddirection of the exhaust gas into the exhaust feed port) is enhancedwhile the flow of the exhaust gas is uniformly suppressed by thearc-shaped taper slope. As a result, the tendency of the exhaust gasflowing biasedly and relatively much to outward of the curved directionis effectively corrected without causing lateral bias.

Further, it is preferable in the invention that a step is formed midwayon a gradient of the taper slope, said step being arcuate concentricallyof an arc shape of said taper slope and projecting toward the entry endface of the aftertreatment device. Then, when the exhaust gas containsan additive having greater specific gravity than the exhaust gas, theadditive flowing along an inner wall surface of the flow passage outwardof the curved direction by a centrifugal force is caused to run ontosaid step, whereby the additive is broken away from the inner wallsurface of the flow passage and is diffused toward the entry end face ofthe aftertreatment device. Thus, the additive whose bias has beendifficult to be corrected can be substantially improved indispersibility.

Further, it is preferable in the invention that the exhaust conduit hasa flow passage cross section upstream of the exhaust feed port in theform of a rhombus with one of diagonals thereof being aligned with thecurved direction of said exhaust conduit. Then, the flow of the exhaustgas upstream of the exhaust feed port can be guided centrally of theexhaust conduit and be persuaded to form a main flow substantiallycentrally of the exhaust conduit to thereby further suppress generationof lateral bias upon the turnabout of the flow.

Further, it is preferable in the invention that a guide depression isformed on the gas dispersion portion, said guide depression projectinginto the throttling space in position corresponding to a bisectrix of afan shape of the flow guide space to suppress and direct the main flowof the exhaust gas centrally of the entry end face of the aftertreatmentdevice. Then, when the flow rate of the exhaust gas is lowered, the mainflow of the exhaust gas is effectively suppressed and guided centrallyof the entry end face of aftertreatment device by said guide depression.

Further, it is preferable in the invention that a sensor boss is formedon the bisectrix of the fan shape of the flow guide space between theguide depression and the taper slope. Then, the sensor boss can beutilized to position the sensor, which contributes to direct detectionof temperature or other various information on the main flow of theexhaust gas.

Advantageous Effects of Invention

The above-mentioned exhaust emission control device according to theinvention can exhibit various excellent effects as mentioned in thebelow.

(I) Upon turnabout introduction of the exhaust gas into theaftertreatment device, the tendency of the exhaust gas flowingrelatively much and to outward of the curved direction can beeffectively corrected to an extent unattainable ever before, so that afull volume of the aftertreatment device can be effectively utilized tosufficiently derive the catalytic performance to be inherentlyexhibited.

(II) When employed is the construction that the step is formed midway onthe gradient of the taper slope, is arcuate concentrically of an arcshape of said taper slope and projects toward the entry end face of theaftertreatment device, even if the exhaust gas contains the additivehaving greater specific gravity than the exhaust gas, the additiveflowing along the inner wall surface of the flow passage outward of thecurved direction by the centrifugal force can be caused to run onto thestep, whereby the additive is broken away from the inner wall surface ofthe flow passage and is diffused toward the entry end face of theaftertreatment device. Thus, the dispersibility of the additivecontained in the exhaust gas can be substantially improved to furthereffectively derive the catalytic performance of the aftertreatmentdevice.

(III) When employed is the construction that the exhaust conduit has theflow passage cross section upstream of the exhaust feed port in the formof the rhombus with one of the diagonals thereof being aligned with thecurved direction of said exhaust conduit, the formation of the flowpassage cross section upstream of the exhaust feed port in the exhaustconduit in the form of the rhombus guides the flow of the exhaust gasupstream of the exhaust feed port centrally of the exhaust conduit topersuade formation of the main flow thereof substantially centrally ofthe exhaust conduit, thereby further suppressing generation of lateralbias upon turnabout of the flow, leading to further effective derivationof the catalytic performance of the aftertreatment device.

(IV) When employed is the construction that the guide depression isformed on the gas dispersion portion and projects into the throttlingspace in position corresponding to the bisectrix of the fan-shape of theflow guide space to suppress and direct the main flow of the exhaust gascentrally of the entry end face of the aftertreatment device, even ifthe flow rate of the exhaust gas is lowered to lower the suppressiveeffect of the taper slope, the main flow of the exhaust gas can beeffectively suppressed by the guide depression to guide the samecentrally of the entry end face of the aftertreatment device to therebycompensate lowering of the catalytic performance due to lowering in flowrate of the exhaust gas.

(V) When employed is the construction that the sensor boss is formed onthe bisectrix of the fan shape of the flow guide space between the guidedepression and the taper slope, the sensor boss can be utilized toposition the sensor, which contributes to direct detection oftemperature or other various information on the main flow of the exhaustgas, leading to substantial enhancement of the detection accuracy andrealization of easily arranging the sensor in position.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram showing an example of a conventionalexhaust emission control device;

FIG. 2 is a perspective view showing an embodiment of the invention;

FIG. 3 is a front view of a gas dispersion portion shown in FIG. 2;

FIG. 4 is a view looking in a direction of arrows IV in FIG. 3;

FIG. 5 is a sectional view looking in a direction of arrows V in FIG. 4;and

FIG. 6 is a sectional view of the gas dispersion portion shown in FIG.4.

DESCRIPTION OF EMBODIMENT

An embodiment of the invention will be described in conjunction with thedrawings.

FIGS. 2-6 show the embodiment of the invention. In the embodimentrelating to an exhaust emission control device constructed similar tothat explained in the above with respect to FIG. 1, a gas dispersionportion 7C providing a downstream portion of the communication passage 7is constructed such that it covers an entry end face of a selectivereduction catalyst 4 as aftertreatment device and that the exhaust gas 1is introduced through an exhaust feed port 11 from a directionsubstantially perpendicular to an axis of the catalyst 4 (see FIG. 4). Amixing pipe 7B guiding the exhaust gas 1 into the exhaust feed port 11of the gas dispersion portion 7C provides an exhaust conduit curved fromthe exhaust feed port 11 toward an exit side of the selection reductioncatalyst 4 to extend axially of the selection reduction catalyst 4. Thegas dispersion portion 7C is of a crushingly deformed shape to ensure anarea extending from the exhaust feed port 11 to a vicinity of anextension of the axis of the selective reduction catalyst 4 in the gasdispersion portion 7C as a fan-likely spreading flow guide space 12, aremaining area being a flat throttling space 13 close to the entry endface of the selective reduction catalyst 4, a boundary between thethrottling and flow guide spaces 13 and 12 in the crushingly deformedshape being formed as an arc-like taper slope 14.

Especially in the embodiment, formed midway on a gradient of the taperslope 14 is a step 15 which is arcuate concentrically of an arc shape ofthe taper slope 14 and projects or jetties toward the entry end face ofthe selective reduction catalyst 4; and the mixing pipe 7B has a flowpassage cross section upstream of the exhaust feed port 11 in the formof a rhombus with one of diagonals thereof being aligned with the curveddirection of the mixing pipe 7B (see FIG. 5).

Formed on the gas dispersion portion 7C is a guide depression 16 whichprojects into the throttling space 13 in position corresponding to abisectrix X of the fan shape of the flow guide space 12 (see FIG. 3) tosuppress and direct a main flow of the exhaust gas 1 centrally of theentry end face of the selective reduction catalyst 4. Formed on thebisectrix X (see FIG. 3) of the fan shape of the flow guide space 12 andbetween the guide depression 16 and the taper slope 14 is a sensor boss17 into which a sensor 18 is fitted to detect a temperature of theexhaust gas 1.

In this way, the exhaust gas 1 guided through the mixing pipe 7B ischanged in direction into the direction substantially perpendicular tothe axis of the selective reduction catalyst 4 and is introduced intothe exhaust feed port 11. While flowing from the exhaust feed port 11into the flow guide space 12 widened fan-likely, the exhaust gas 1 isenhanced in dispersibility in the lateral direction (directionsubstantially parallel to the entry end face of the selective reductioncatalyst 4 and substantially perpendicular to the introduction directionof the exhaust gas 1) and is evenly suppressed in flow by the arc-shapedtaper slope 14. Thus, the tendency of the exhaust gas 1 flowing biasedlyand relatively much to outward of the curved direction is correctedeffectively without causing any lateral bias.

In a case of an exhaust emission control device having, as theaftertreatment device, the selective reduction catalyst 4 as disclosedin the embodiment, the exhaust gas 1 contains misty urea water(additive) added upstream. The misty urea water, which has greaterspecific gravity than the exhaust gas 1, tends to be prominently biasedto outward of the curved direction. However, the formation, midway onthe gradient of the taper slope 14, of the step 15 which is arcuateconcentrically of the arc shape of the taper slope 14 and projects orjetties toward the entry end face of the selective reduction catalyst 4causes the misty urea water flowing along an inner wall surface of theflow passage outward of the curved direction by a centrifugal force torun onto the step 15, whereby the misty urea water is broken away fromthe inner wall surface of the flow passage and is diffused toward theentry end face of the selective reduction catalyst 4. Thus, the mistyurea water whose bias has been difficult to be corrected can besubstantially enhanced in dispersibility.

Thus, according to the above-mentioned embodiment, upon turnaboutintroduction of the exhaust gas 1 into the selective reduction catalyst4, the tendency of the exhaust gas 1 flowing relatively much to outwardof the curved direction thereof can be effectively corrected to anextent unattainable ever before, so that a full volume of the selectivereduction catalyst 4 can be effectively utilized to sufficiently derivethe catalytic performance to be inherently exhibited. Even if the mistyurea water, which has greater specific gravity than the exhaust gas 1,is contained in the exhaust gas 1, the misty urea water flowing alongthe inner wall surface of the flow passage outward of the curveddirection by the centrifugal force is caused to run onto the step 15 sothat the misty urea water can be broken away from the inner wall surfaceof the flow passage and be diffused toward the entry end face of theselective reduction catalyst 4. Thus, the dispersibility of the mistyurea water contained in the exhaust gas 1 can be also substantiallyenhanced, leading to further effective derivation of the catalyticperformance of the selective reduction catalyst 4.

Further, in the embodiment, the mixing pipe 7B has the flow passagecross section upstream of the exhaust feed port 11 in the form of therhombus with one of the diagonals thereof being aligned with the curveddirection of the mixing pipe 7B. Thus, the flow of the exhaust gas 1upstream of the exhaust feed port 11 can be guided centrally of themixing pipe 7B and persuaded to form a main flow substantially centrallythereof to thereby further suppress generation of lateral bias uponturnabout of the flow, leading to further effective deviation of thecatalytic performance of the selective reduction catalyst 4.

Moreover, the guide depression 16 is formed in the gas dispersionportion 7C, so that, even if the flow rate of the exhaust gas 1 islowered to lower the suppressive effect of the taper slope 14, the mainflow of the exhaust gas 1 can be effectively suppressed by the guidedepression 16 to guide the same centrally of the entry end face of theselective reduction catalyst 4 to thereby compensate lowering of thecatalytic performance due to lowering in flow rate of the exhaust gas 1.

Further, in the embodiment, the sensor boss 17 is formed on thebisectrix of the fan shape of the flow guide space 12 between the guidedepression 16 and the taper slope 14 so that the sensor boss 17 can beutilized to position the sensor 18, which contributes to directdetection of the temperature of the main flow of the exhaust gas 1,leading to substantial enhancement of the detection accuracy andrealization of easily arranging the sensor 18 in position.

It is to be understood that an exhaust emission control device accordingto the invention is not limited to the above embodiment and that variouschanges and modifications may be made without departing from the scopeof the invention. For example, though the embodiment illustrated isapplication to an entry side of a selective reduction catalyst in anarrangement thereof in parallel with a particulate filter, the inventionmay be similarly applied to any aftertreatment device other than theselective reduction catalyst; alternatively, the invention may beapplied to a variety of types of exhaust emission control devices withadopted layout of turnabout introduction of exhaust gas into anaftertreatment device.

REFERENCE SIGNS LIST

-   1 exhaust gas-   4 selective reduction catalyst (aftertreatment device)-   7B mixing pipe (exhaust conduit)-   7C gas dispersion portion-   11 exhaust feed port-   12 flow guide space-   13 throttling space-   14 taper slope-   15 step-   16 guide depression-   17 sensor boss

1. An exhaust emission control device with an exhaust system includingan aftertreatment device for purifying exhaust gas passing therethroughand with an adopted layout for turnabout introduction of the exhaust gasinto said aftertreatment device, characterized in that it comprises agas dispersion portion for covering an entry end face of saidaftertreatment device and for introducing the exhaust gas thereintothrough an exhaust feed port from a direction substantiallyperpendicular to an axis of said aftertreatment device and an exhaustconduit curved from the exhaust feed port in said gas dispersion portiontoward an exit side of said aftertreatment device to extend axially ofsaid aftertreatment device, said gas dispersion portion being of acrushingly deformed shape to ensure an area from said exhaust feed portin said gas dispersion portion to a vicinity of an extension of the axisof said aftertreatment device as a fan-likely spreading flow guidespace, a remaining area being a flat throttling space close to the entryend face of said aftertreatment device, a boundary between saidthrottling and flow guide spaces in the crushingly deformed shape beingformed as an arc-like taper slope.
 2. The exhaust emission controldevice as claimed in claim 1, wherein a step is formed midway on agradient of the taper slope, the step being arcuate concentrically of anarc shape of said taper slope and projecting toward the entry end faceof the aftertreatment device.
 3. The exhaust emission control device asclaimed in claim 1, wherein the exhaust conduit has a flow passage crosssection upstream of the exhaust feed port in the form of a rhombus withone of diagonals thereof being aligned with the curved direction of saidexhaust conduit.
 4. The exhaust emission control device as claimed inclaim 2, wherein the exhaust conduit has a flow passage cross sectionupstream of the exhaust feed port in the form of a rhombus with one ofdiagonals thereof being aligned with the curved direction of saidexhaust conduit.
 5. The exhaust emission control device as claimed inclaim 1, wherein a guide depression is formed on the gas dispersionportion, said guide depression projecting into the throttling space inposition corresponding to a bisectrix of a fan shape of the flow guidespace to suppress and direct a main flow of the exhaust gas centrally ofthe entry end face of the aftertreatment device.
 6. The exhaust emissioncontrol device as claimed in claim 2, wherein a guide depression isformed on the gas dispersion portion, said guide depression projectinginto the throttling space in position corresponding to a bisectrix of afan shape of the flow guide space to suppress and direct a main flow ofthe exhaust gas centrally of the entry end face of the aftertreatmentdevice.
 7. The exhaust emission control device as claimed in claim 3,wherein a guide depression is formed on the gas dispersion portion, saidguide depression projecting into the throttling space in positioncorresponding to a bisectrix of a fan-shape of the flow guide space tosuppress and direct a main flow of the exhaust gas centrally of theentry end face of the aftertreatment device.
 8. The exhaust emissioncontrol device as claimed in claim 4, wherein a guide depression isformed on the gas dispersion portion, said guide depression projectinginto the throttling space in position corresponding to a bisectrix of afan-shape of the flow guide space to suppress and direct a main flow ofthe exhaust gas centrally of the entry end face of the aftertreatmentdevice.
 9. The exhaust emission control device as claimed in claim 5,wherein a sensor boss is formed on the bisectrix of the fan shape of theflow guide space between the guide depression and the taper slope. 10.The exhaust emission control device as claimed in claim 6, wherein asensor boss is formed on the bisectrix of the fan shape of the flowguide space between the guide depression and the taper slope.
 11. Theexhaust emission control device as claimed in claim 7, wherein a sensorboss is formed on the bisectrix of the fan shape of the flow guide spacebetween the guide depression and the taper slope.
 12. The exhaustemission control device as claimed in claim 8, wherein a sensor boss isformed on the bisectrix of the fan shape of the flow guide space betweenthe guide depression and the taper slope.